This invention generally relates to techniques for fabricating an object. More particularly, the present invention provides a method for fabricating a switch fabric using one or more semiconductor processing techniques. Merely by way of example, the present invention is implemented using such method for a fabric in a wide area network for long haul telecommunications, but it would be recognized that the invention has a much broader range of applicability. The invention can be applied to other types of networks including local area networks, enterprise networks, small switch designs (e.g., two by two or greater) and the like.
As a need for additional switching channels increases, it becomes more desirable to have larger and larger switching devices. Such switching devices must often be capable of switching a beam from one optical fiber to one of a plurality of optical fibers, which can include hundreds of such fibers. Integration of such optical fibers and switching a single beam from one fiber to another fiber is often a difficult task by way of a purely optical technique. Accordingly, there have been many attempts to make commercial devices that require the need to convert optical signals from a first source into electric signals for switching such optical signals over a communication network. Once the electric signals have been switched, they are converted back into optical signals for transmission over the network.
Numerous limitations exist with such conventional electrical switching technique. For example, such electrical switching often requires a lot of complex electronic devices, which make the device difficult to scale. Additionally, such electronic devices become prone to failure, thereby influencing reliability of the network. The switch is also slow and is only as fast as the electrical devices. Accordingly, techniques for switching optical signals using a purely optical technology have been proposed. Such technology can use a wave-guide approach for switching optical signals. Unfortunately, such technology has been difficult to scale and to build commercial devices. Other companies have also been attempting to develop technologies for switching high number of signals in other ways, but have been generally limited.
For example, Petersen forms a two-dimensional mirror structure with relatively large design dimensions. We understood that the design dimensions of Petersen were much greater than what is required for high-density integrated designs of hundreds of devices and greater. Additionally, Petersen has been effective in forming one or more mirror devices from a substrate fabric. Such devices often cannot be scaled up to form large arrays of such mirror devices. Petersen also has limitations in that the deflection devices warp with optical coatings. Additionally, such devices had poor frequency response and operation characteristics. A way of controlling device thickness and torsion bar thickness also posed a problem. These and other limitations are described throughout this specification and more particularly below.
From the above, it is seen that an improved way to fabricate deflection devices is highly desirable.
According to the present invention, a technique including a method for fabricating an object such as a switch fabric is provided. More particularly, the invention provides a method using one or more semiconductor processing techniques. Merely by way of example, the present invention is implemented using such method for a fabric in a wide area network for long haul telecommunications, but it would be recognized that the invention has a much broader range of applicability. The invention can be applied to other types of networks including local area networks, enterprise networks, small switch designs (e.g., two by two or greater) and the like.
In a specific embodiment, the invention provides a method for fabricating a mirror array from a silicon on insulator substrate structure. The method includes providing a silicon-on-insulator (SOI) substrate structure, which may have a material thickness of greater than 10 microns overlying an insulating layer, although the substrate structure can be made of other materials. The SOI material thickness is of a single crystal silicon bearing material. The method also patterns the material thickness using a deep reactive ion etching process to pattern a mirror device structure by forming a trench region that extends from a surface of the material thickness to the insulator structure; and patterns the thickness of material to form a recessed region coupled to the trench region to define a torsion bar structure. The recessed region extends from the surface of the material thickness toward the insulator structure and has a depth that is more than about 20% of the mirror device thickness in a preferred embodiment. The method forms an opening on a back side of the SOI substrate structure to the insulator structure. The method removes the insulator material to release the mirror device structure and the torsion bar structure.
Many benefits are achieved by way of the present invention over conventional techniques. The invention provides an easy and efficient way of manufacturing high density mirror arrays, e.g., 500 sites, 550 sites, 1000 sites, 4000 sites, and greater. The present invention also can use conventional process technology, which makes it efficient to make and use it. By way of the silicon on insulator substrate, the invention provides an etch stop using the insulator layer sandwiched between semiconductor layers. In some embodiments, the invention uses epitaxial silicon as a mirror layer, which is high quality single crystal silicon. In most embodiments, the present method is efficient. Depending upon the embodiment, one or more of these benefits may be achieved.
Various additional objects, features and advantages of the present invention can be more fully appreciated with reference to the detailed description and accompanying drawings that follow.